This invention relates to a thermostatic working element having a housing for receiving an expansion medium in which an electric heating element is arranged which is provided with connecting lines which are guided to the outside in a base which surrounds them and closes an opening of the bottom of the housing, and to a process for bringing an electric heating element into a housing.
In particular, such a thermostatic working element is used particularly with a thermostatic valve as it is known from German Patent Document DE 42 33 913 A1.
An electrically heated, thermostatic working element is known (European Patent Document EP 0 139 586 A1) in which an opening of the bottom of the housing is closed by means of a base made of plastic which surrounds the connecting lines of the heating element and through which the connecting lines are guided to the outside. The base is produced as a separate component. It is inserted from the outside into an opening of the housing having a ring shoulder with the interposition of a sealing ring and is held by means of a flanging of the outer edge of the opening.
It is an object of the invention to provide a construction which is as simple as possible and offers a high measure of tightness against an emerging of the expansion medium.
This object is achieved in that the base is injected molded into the opening of the bottom of the housing.
The mounting of an injected base has the advantage that the base is already mounted when it is manufactured without requiring any additional mounting operations for bringing in and adapting the base. In addition, such an injected base, in a simple manner, can be designed such that a very high measure of tightness is obtained.
According to certain preferred embodiments of the invention, it is provided that the base injected into the bottom projects to the outside by means of a projection surrounding the connecting lines. As a result, it is achieved that, on the one hand, the connecting lines are surrounded by the injected base along a relatively large length which leads to a high measure of tightness while, on the other hand, the connecting lines are held in a very secure manner so that the fastening points between the connecting lines and the heating element are relieved from tensile forces which are exercised on the connecting lines.
In a further development of preferred embodiments of the invention, it is provided that the injected-molded-on base frames an edge of the heating element which faces the bottom of the housing. As a result, the heating element is also held by the injected base and is fixed in the housing.
In an expedient further development of preferred embodiments of the invention, it is provided that the base covers the bottom in the interior of the housing. Thus, relatively large sealing surfaces are obtained between the base and the housing. For the same purpose, it is provided in another embodiment that, in the interior of the housing, the base covers an edge area of the interior wall of the housing which adjoins the bottom.
In a further development of preferred embodiments of the invention, it is provided that the opening of the bottom is provided with at least one surrounding annular groove which is filled by the material of the injected base. This results in the form-locking connection between the injected base and the housing while, in addition, the sealing surfaces are enlarged once again.
In a further development of preferred embodiments of the invention, it is provided that the base injected into the opening of the bottom of the housing is made in one piece with a cap framing the housing on the outside. By means of such a molded-on cap, the tightness can be improved further, on the one hand, while, on the other hand, the effective sensing surface of the housing of the thermostatic working element can be determined by dimensioning the axial length of the cap. In the case of an advantageous further development, it is provided that the cap is equipped with at least one receiving device for an additional element. Such an additional element may, for example, be a sealing ring or the like.
In a further development of preferred embodiments of the invention, it is provided that the area of the base facing the interior of the housing is provided with a sealing mass adjoining the interior wall of the housing and/or the outer surfaces of the supporting body. This sealing mass, which is a preferably adhesive plastic material which can be polymerized out, results in a further increase of the tightness by means of the additional sealing mass which has permanently elastic characteristics and which ensures the tightness also for an extended useful life of the thermostatic working element.
In a further development of preferred embodiments, the invention relates to a process for bringing an electric heating element into a housing of a thermostatic element which is characterized in that the heating element provided with the connecting lines is held in a core which embeds it and is introduced into the housing together with the core, in which case the core, the housing and a mold part are joined to form a casting mold into which a base made of plastic is injected which closes the recess of the bottom and surrounds the connecting lines.
In a further development of preferred embodiments of the invention, it is provided that, before the injection of the base, the walls of the housing and/or the surface of the heating element are provided with an adhesion promoting substance by spraying or otherwise applying the adhesive promoting substance. This adhesion promoting substance has the result that an adhesive connection is provided between the injected base and the walls of the housing and/or the supporting body of the heating element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.